In a typical integrated circuit manufacturing process flow, metal is deposited onto a patterned dielectric (typically a silicon dioxide based material) to fill the vias and trenches formed in the dielectric layer. The resulting metallization layer is typically formed either directly on a layer carrying active devices (e.g., transistors), or on another metallization layer. The resulting metal-filled vias and trenches form the conductive pathways of an integrated circuit (IC) device. Contacts and interconnects are formed between active devices and metal-filled vias as well as between metal lines of adjacent metallization layers.
Fabrication of contacts and interconnects involves a contact-precleaning operation, which is usually performed after inter-layer dielectric (ILD) has been patterned to provide vias and trenches, but before the vias and trenches are filled with metal. Contact precleaning removes materials that can interfere with good contact between metal lines of adjacent metallization layers, or between metal lines and active devices. One of materials that may be difficult to remove during contact precleaning is silicon nitride, which is often used in IC fabrication as an etch stop layer. Currently there is a need for methods of removing silicon nitride from interconnects and contact holes.